Safety and Hazards
What is the difference between a hazard and a precaution?
A hazard can cause harm. A precaution reduces the risk of harm.
Describe the arrangement and movement of particles in a solid.
The particles are close together in fixed positions, and they vibrate.
What happens to particle energy and movement when a liquid freezes?
The particles lose energy, slow down, and become fixed in position.
What is a pure substance?
A pure substance contains only one type of particle.
In salty water, identify the solute and the solvent.
Salt is the solute. Water is the solvent.
A chemical spills on the bench. What should you do first?
Tell the teacher immediately, keep away, and follow the teacher's instructions.
Why can a liquid flow and take the shape of its container?
Its particles are close together but can move past one another.
Explain evaporation and condensation as opposite changes of state.
Evaporation changes a liquid into a gas. Condensation changes a gas into a liquid.
What is a mixture?
A mixture contains two or more substances physically combined. Each substance keeps its properties and can be separated.
Where does sugar go when it dissolves completely in water?
The sugar particles spread evenly between the water particles. They have not disappeared; the mixture is a solution.
A bottle carries the GHS flame pictogram. What does it warn about, and what should it be kept away from?
It warns that the substance is flammable. Keep it away from flames, sparks, and heat.
Why can a gas be compressed into a smaller space?
Gas particles have large gaps between them, so they can be pushed closer together.
What is diffusion?
Diffusion is the spreading of particles from a region of high concentration to low concentration until they are more evenly spread.
Classify sea water as pure or a mixture, and explain.
Sea water is a mixture because it contains water and dissolved salts, so it has more than one type of particle.
What is a saturated solution?
It is a solution in which the maximum amount of solute has dissolved at that temperature. Extra solute remains undissolved.
An open acid bottle could spill and burn someone. Identify the hazard, the risk, and one precaution.
Hazard: the open acid. Risk: a spill could burn skin. Precaution: close and store the bottle safely.
Why does compressing a gas increase its pressure?
The particles have less space and collide with the container walls more often, so pressure increases.
Why does perfume diffuse faster in a warm room than in a cold room?
Warm particles have more energy and move faster, so their random movement spreads the perfume more quickly.
A material contains two different particle types mixed together. Is it pure or a mixture? Explain.
It is a mixture because it contains more than one type of particle.
How can you tell a suspension from a solution?
A suspension is cloudy and its undissolved particles may settle. A solution is evenly mixed and usually clear.
A student heats a flammable liquid beside an open flame. State the main hazard and give two suitable precautions.
The flammable liquid could catch fire. Remove the open flame, use an approved heat source, wear eye protection, and work under teacher supervision. Any two suitable precautions earn the points.
A sealed syringe of air is pushed from 20 mL to 10 mL. Explain what happens to particle spacing, collisions, and pressure.
The particles are pushed closer together, collide with the syringe walls more often, and the pressure increases.
A drop of food coloring is added to cold water and warm water. Predict the difference and explain it using particles.
It spreads faster in warm water because warmer particles have more energy and move faster, increasing the rate of diffusion.
A sample contains identical molecules, and every molecule has two bonded types of atom. Is the sample pure or a mixture? Explain.
It is a pure compound because every particle is the same, even though each molecule contains two elements.
Compare a saturated solution with a suspension using dissolving, appearance, and settling.
A saturated solution has dissolved the maximum solute and may have extra solid left. A suspension contains undissolved particles, looks cloudy, and settles over time.